WASHINGTON – As the Supreme Court prepares to take up same-sex marriage next week, conservative scholars have produced a last-ditch argument to keep the scourge of homosexual unions from spreading across the land: Gay marriage kills.

The logic is about as obvious as if they had alleged that raising the minimum wage would increase the frequency of hurricanes. If anything, you’d think that more same-sex marriages would mean more adoptions.

But comes now Gene Schaerr, unsuccessful lawyer for Utah in that state’s case against same-sex marriages, to file an amicus brief with the Supreme Court on behalf of “100 scholars of marriage.”

“On the surface, abortion and same-sex marriage may seem unrelated,” Schaerr acknowledged in a post on the Heritage Foundation website in advance of a presentation he made to the conservative think tank Monday. But “the two are closely linked in a short and simple causal chain.”

To wit: Legalizing same-sex marriage devalues marriage and causes fewer heterosexual couples to marry, which leads to a larger number of unmarried women, who have abortions at higher rates than married women. As a result, Schaerr wrote, “nearly 900,000 more children of the next generation would be aborted as a result of their mothers never marrying.”

Case closed! Or at least it would be, if Schaerr’s “causal chain” were real. He freely acknowledged that he had no cause-and-effect proof when I asked him about it at Heritage on Monday.

“It is still too new to do a rigorous causation analysis using statistical methods,” he admitted, saying that he had found only a decline in marriage rates in states that had legalized same-sex marriage (in fact, marriage rates have declined overall). “The brief doesn’t even attempt to say conclusively that this reduction in marriage rates has been the result of adopting same-sex marriage,” Schaerr said, though there are “theoretical reasons” such causation might occur.

Or perhaps theological reasons. When Schaerr quit his law firm last year to take the Utah case, he wrote to colleagues that he was going to “fulfill what I have come to see as a religious and family duty.” A colleague leaked his resignation letter to the Human Rights Campaign, a gay-rights group.

Utah argued that legalizing same-sex marriage would lead to lower birth rates, pointing out that some of the states with the lowest birth rates, such as Massachusetts, Vermont and Connecticut, had same-sex marriage, and some of the highest birth-rate states, such as Texas and Utah, did not.

But the national birth rate has been declining for years, from 14.3 per 1,000 people in 2006 to 12.4 in 2013. Texas and Utah actually had larger drops than Massachusetts, Vermont and Connecticut.

Utah lost its case, but Schaerr — a former clerk to Antonin Scalia — is now making a similar argument, claiming to show drops in marriage rates in the years after states adopted same-sex marriage.

Heritage’s Ryan Anderson, appearing with Schaerr, went even further than Schaerr’s conclusions in alleging that “every nation and every state that have redefined marriage have seen their marriage rates decline by at least 5 percent after that redefinition, even as the marriage rates in the rest of the states remain stable.”

Oh?

The national marriage rate declined to 6.8 per 1,000 in 2012, from 8 in 2002, before Massachusetts became the first state to legalize gay marriage. The Massachusetts rate dropped from 5.9 in 2002 to 5.5 in 2011, while Connecticut went from 5.7 to 5.5 and Vermont went from 9.8 to 8.3. But Texas and Utah, free of same-sex marriage, dropped from 8.4 to 7.1, and from 10.4 to 8.6, respectively.

Though the numbers are dubious, Schaerr’s argument has the useful purpose of switching the debate away from same-sex marriage — on which public opinion is shifting decidedly against conservatives — and toward abortion, where positions are hardened.

Schaerr had other arguments, too. He asserted that Abraham Lincoln would find it “preposterous” that the 14th Amendment, guaranteeing equal protection, would be used to justify same-sex marriage.

What Lincoln would think in 2015 is unknowable — but such considerations did not deter Schaerr. He also speculated that an unemployed man who got his girlfriend pregnant in a state that had legalized same-sex marriage would be more likely to conclude that “I’m not going to assume these obligations to this woman and this child.”

From that idle speculation, all it takes is a slippery slope and an active imagination to get to 900,000 abortions.